Brake master cylinder with return connection

ABSTRACT

A brake master cylinder (10) for a hydraulic vehicle brake system has a master cylinder housing (32) and at least one pressure chamber (40) designed therein. Connected to the pressure chamber (40) is a hydraulic fluid reservoir which, furthermore, is provided for connection to a precharge pump of a brake pressure regulating system. Moreover, the brake master cylinder (10) has a hydraulic fluid return connection (30) which makes a fluid connection between the delivery side of the precharge pump, the reservoir and the at least one pressure chamber (40). A throttle (60) is arranged in this liquid connection, said throttle not impeding a hydraulic fluid stream out of the reservoir into the at least one pressure chamber (40) and throttling a hydraulic fluid stream from the return connection (30) into the reservoir. The throttle (60) makes it possible to cause the precharge pump to act on the at least one pressure chamber (40), without an electromagnetic valve being interposed.

The invention relates to a brake master cylinder for a hydraulic vehiclebrake system according to the preamble of patent claim 1. The inventionrelates, in particular, to a brake master cylinder suitable forinteracting with a brake pressure regulating system which comprisestraction control and/or driving dynamics control. Such a brake mastercylinder is known from DE 41 12 134 A1 which describes awheelslip-controlled hydraulic brake system for automobiles.

Hydraulic vehicle brake systems are nowadays often equipped with a brakepressure regulating system which is intended, above all, to prevent thewheels of the vehicle from locking in the event of very sharp braking. Abrake pressure regulating system of this type is usually referred to asan antilock system. Increasingly, however, the capabilities inherent insuch a brake pressure system are also used for preventing or at leastlimiting the spin of driven vehicle wheels which may occur, inparticular, during acceleration on slippery ground. This is referred toas traction control. Even further developed systems use the brakepressure regulating system in order to neutralize critical vehiclestates, for example an imminent swerving of a vehicle on a bendapproached too quickly. For this purpose, signals from various sensorsare processed, which give information on instantaneous variables, suchas, for example, driving speed, steering angle lock, transverseacceleration and other parameters describing the instantaneous drivingstate, whereupon, when a hazardous driving state is detected, the systemattempts to eliminate this hazardous driving state, inter alia bycontrolled braking actions on individual wheels. Such systems aredesignated as driving dynamics controls. A fundamental differencebetween a brake pressure regulating system designed only for antilockbraking and a brake pressure regulating system which is employed,furthermore, for traction control or driving dynamics control is thatthe latter must be capable of building up brake pressure when the brakemaster cylinder is both actuated and not actuated, since the vehicledriver himself does not actuate the brake when traction control ordriving dynamics control is taking effect.

Conventional brake pressure regulating systems have a so-called returnpump which is designed for high pressure and a small volumetric flow andis not selfpriming. The hydraulic fluid therefore has to be supplied tothe return pump under a particular admission pressure. In brake pressureregulating systems designed only for antilock braking, the pressuregenerated by the driver in the brake master cylinder by actuating thebrake pedal is, under certain circumstances, sufficient for thispurpose. If, however, the brake pressure regulating system is also to beemployed for traction control and/or driving dynamics control, theremust be a so-called precharge pump which can provide the return pumpwith sufficient admission pressure even when the brake master cylinderis not actuated. The installation of a precharge pump in a brakepressure regulating system normally requires a plurality ofelectromagnetic valves.

The object on which the invention is based is to simplify brake pressureregulating systems with a traction control and/or driving dynamicscontrol function.

Proceeding from a brake master cylinder of the type initially mentioned,this object is achieved, according to the invention, in that a throttleis arranged in the fluid connection, existing in the installed state ofthe brake master cylinder, between the delivery side of the prechargepump, the reservoir and the at least one pressure chamber, said throttlenot impeding a hydraulic fluid stream out of the reservoir into the atleast one pressure chamber and throttling a hydraulic fluid stream fromthe return connection to the reservoir. By virtue of the common fluidconnection between the delivery side of the precharge pump, thereservoir and the at least one pressure chamber in the master cylinderhousing, according to the invention the precharge pump acts directly onthe at least one pressure chamber and thereby ensures that there is aparticular admission pressure in at least the brake circuit which isconnected to the one pressure chamber. The direction-dependent throttleon the one hand allows an unimpeded hydraulic fluid stream out of thereservoir into the at least one pressure chamber, but, on the otherhand, due to its throttling effect in the opposite direction of flow,that is to say from the return connection to the reservoir, ensuresthat, during operation, the precharge pump can build up a specificadmission pressure in the at least one pressure chamber of the brakemaster cylinder. In the solution according to the invention, it ispossible to dispense with an electromagnetic valve in a hydraulic lineleading from the delivery side of the precharge pump to the reservoir,said electromagnetic valve being necessary in conventional systems. Aparticular feature of all the exemplary embodiments according to theinvention is that the pressure generated by the precharge pump can actdirectly on the at least one pressure chamber of the brake mastercylinder and consequently-directly on at least one brake circuit, thusmaking it possible to combine a brake master cylinder according to theinvention with a brake pressure regulating system which does not itselfcomprise a precharge pump, so that the brake pressure regulating systemcan also be provided with a traction control and/or driving dynamicscontrol function at relatively low outlay.

In one exemplary embodiment of a brake master cylinder according to theinvention, the return connection, the one pressure chamber and thereservoir are arranged in this order one behind the other in thedirection of flow of the hydraulic fluid stream and the throttle isarranged between the one pressure chamber and the reservoir. Preferably,in this exemplary embodiment, the throttle is arranged in the onepressure chamber, that is to say the hydraulic fluid stream is led fromthe precharge pump via the return connection into the one pressurechamber and is prevented, by the throttle arranged therein, from flowingfurther, without any delay, out of the pressure chamber into thereservoir. In this last mentioned exemplary embodiment, the throttlemay, for example, be connected to a primary piston arranged in the onepressure chamber, in such a way that said throttle can be displacedtogether with the primary piston.

In another exemplary embodiment of a brake master cylinder according tothe invention, the return connection is connected to an annular spacewhich precedes the one pressure chamber and which is itself connected tothe one pressure chamber and to the reservoir. The connection betweenthe annular space and the one pressure chamber is made, for example, bymeans of a central valve which is arranged in the primary piston of thebrake master cylinder and which is open in its position of rest which itassumes when the brake master cylinder is not actuated. In thisexemplary embodiment, therefore, the reservoir, the one pressure chamberand the return connection each have a fluid connection to the annularspace and the throttle is arranged between the reservoir and the annularspace. In this case, the throttle may be suitably integrated into thebrake master cylinder, for example into a line leading from the annularspace to the reservoir and designed in the master cylinder housing, butit may also be arranged in a nipple of the reservoir, for example in theform of an insert pushed into the nipple.

In yet another exemplary embodiment of a brake master cylinder accordingto the invention, the throttle is arranged in an adaptor piece which islocated between the reservoir and the master cylinder housing and whichcomprises the return connection. This solution according to theinvention is highly cost-effective, since no change has to be made onbrake master cylinder versions already produced. Furthermore, such asolution ensures the highest possible flexibility, since, depending onthe desired outfitting of a vehicle, either the adaptor piece can beused or, instead of the latter, there can be an intermediate piece whichmerely bridges the overall height of the adaptor piece without anyfurther function.

Several exemplary embodiments of the brake master cylinder according tothe invention are explained in more detail below with reference todiagrammatic Figures of which:

FIG. 1 shows a basic diagram of a brake master cylinder according to theinvention which is combined with a precharge pump and with a brakepressure regulating system,

FIG. 2 shows a longitudinal section through a first exemplary embodimentof a brake master cylinder according to the invention,

FIG. 3 shows an enlarged illustration of part of FIG. 2,

FIG. 4 shows a longitudinal section through a second exemplaryembodiment of a brake master cylinder according to the invention,

FIG. 5 shows a detail from FIG. 4 in an enlarged illustration,

FIG. 6 shows a section through a nipple of a hydraulic fluid reservoiraccording to a third exemplary embodiment of a brake master cylinderaccording to the invention, and

FIG. 7 shows a section through an adaptor piece according to a fourthexemplary embodiment of a brake master cylinder according to theinvention.

FIG. 1 shows diagrammatically a brake master cylinder 10 which isclamped in the conventional way together with a brake booster 12 to forma unit. An actuating force can be introduced via a brake pedal 14 intothis unit consisting of the brake master cylinder 10 and of the brakebooster 12.

Associated with the brake master cylinder 10 is a hydraulic fluidreservoir 16 which is connected to the brake master cylinder 10 in afluid conducting manner via two nipples. A hydraulic line 18 connectsthe reservoir 16 to a precharge pump 20 which supplies the admissionpressure for a return pump (not shown) of a brake pressure regulatingsystem 22 illustrated merely as a box. The precharge pump 20, which, incontrast to the return pump (not shown), is designed for low pressureand a high volumetric flow, has a pressure relief valve 24 which comesinto action when the delivery side of the precharge pump 20 is closedand spills away excess pressure. The precharge pump 20 may alternativelyalso be designed, for example as a vane cell pump with correspondinglylarge gaps, in such a way that it deals readily with operatingconditions occurring when the delivery side is closed. There is then noneed for the pressure relief valve 24. On the delivery side, theprecharge pump 20 is connected via a hydraulic line 26 having anonreturn valve 28, on the one hand, to the brake pressure regulatingsystem 22 and, on the other hand, via a return connection 30 to thebrake master cylinder 10.

A first embodiment of a brake master cylinder 10 is shown in more detailin FIGS. 2 and 3. The brake master cylinder 10 has a master cylinderhousing 32 with a longitudinal bore 34, in which a first pressurepiston, designated as a primary piston 36, and a second pressure piston,designated as a secondary piston 38, are sealingly arranged. A firstpressure chamber 40 is delimited in the longitudinal bore 34 between theprimary piston 36 and the secondary piston 38, said pressure chamberbeing connectable to a first brake circuit of the vehicle brake systemvia an outlet (not shown). The secondary piston 38 and the housing-innerend of the longitudinal bore 34 similarly delimit a second pressurechamber 42 which is connectable to a second brake circuit of the vehiclebrake system. The pistons 36 and 38 are prestressed by restoring springs44 and 46 into their initial position which they assume when the brakemaster cylinder 10 is in the nonactuated state and which is illustratedin FIGS. 2 and 3.

The hydraulic fluid reservoir 16, not illustrated in FIGS. 2 and 3,engages with its two nipples into correspondingly shaped connectingorifices 48 and 50 of the master cylinder housing 32. Hydraulic fluidcan then pass out of the reservoir 16 through the connecting orifice 50on the right in FIG. 2, an adjoining duct 52 and an annular space 54preceding the first pressure chamber 40 and, further, through a centralpassage orifice 56 in the primary piston 36 past a first central valve58 and a throttle 60 which is dependent on the direction of flow, andthe purpose of which will be explained in more detail below, into thefirst pressure chamber 40. Hydraulic fluid can pass out of the reservoir16 through the connecting orifice 48 on the left in FIG. 2 and a hollowcrosspin 62 and, further, through a central passage orifice 64 in thesecondary piston 38 past a second central valve 66 into the secondpressure chamber 42. An actuating force can be introduced into the brakemaster cylinder 10 or into its primary piston 36 via an input rod 68connected to the brake pedal 14, said actuating force displacing theprimary piston 36 and the secondary piston 38, coupled hydraulicallythereto, in the pressure build-up direction, that is to say to the leftin FIG. 2. When the brake master cylinder 10 is actuated, the twocentral valves 58 and 66, which are kept open by butting respectively ona crosspin 70 and the crosspin 62 in the position of rest of the primaryand secondary pistons 36 and 38, close and thus allow pressure to buildup in the pressure chambers 40 and 42.

The throttle 60 dependent on the direction of flow consists functionallyof a nonreturn valve 72 and of a throttle orifice 74 (see FIG. 3). Inthe first exemplary embodiment illustrated in FIG. 3, the throttle 60dependent on the direction of flow is formed by an essentially tubularbasic body 76 which is provided with a passage bore 78 conicallynarrowing in the middle region. The conical narrowing of the passagebore 78 forms the valve seat for a ball 80 of the nonreturn valve 72.The ball 80 is prestressed against the valve seat by means of a spring82. The spring 82 is held by a spring holding plate 84 of U-shapedcross-section which is pressed into that end of the passage bore 78 ofthe basic body 76 which is on the left in relation to FIG. 3. In thefirst exemplary embodiment, the throttle orifice 74 is formed by aradial duct 86 in the basic body 76, said duct extending between theportion of smaller diameter of the passage bore 78 and the outercircumferential surface of the basic body 76. The basic body 76penetrates with its end portion on the right in FIG. 3 into a bore 88 ofthe primary piston 36, the first central valve 58 also being received insaid bore. Arranged displaceably on that end portion of the basic body76 which is on the left in FIG. 3 is a hollow-cylindrical spring collar90, on which the restoring spring 44 of the primary piston 36 issupported. The spring collar 90 has a plurality of radial passages 92which make an unthrottled connection between the first pressure chamber40 and the throttle 60.

The functioning of the brake master cylinder 10 will be explained inmore detail below. It is presupposed, in this case, that the hydraulicline 26 (see FIG. 1) coming from the precharge pump 20 opens into thefirst pressure chamber 40 of the brake master cylinder 10, that is tosay the return connection 30 connects the hydraulic line 26 to the firstpressure chamber 40 (not illustrated in FIGS. 2 and 3).

During normal braking, as already indicated, an actuating force istransmitted to the primary piston 36 via the input rod 68, as a resultof which the two pistons 36 and 38 are displaced to the left, with theconsequence that brake pressure is built up in the pressure chambers 40and 42 after the closing of the central valves 58 and 66 which takesplace during this displacement. When the actuating force introduced viathe input rod 68 lapses after braking has been executed, the restoringsprings 44 and 46 move the pistons 36 and 38 to the right back intotheir initial positions again. Toward the end of this return strokemovement, the two central valves 58 and 66 open and hydraulic fluidflows out of the reservoir 16 along the paths already mentioned aboveinto the pressure chambers 40 and 42. In this case, the throttle 60 doesnot oppose any appreciable resistance to the hydraulic fluid flowinginto the first pressure chamber 40, since the nonreturn valve 72 isprestressed only slightly into its closing position and therefore openseasily. Throttling which is undesirable with regard to this direction offlow of the hydraulic fluid does not take place and the efficiency ofthe brake master cylinder 10 is maintained.

During a normal braking operation just described, the precharge pump 20is not put into operation. This occurs, however, when a control unit,assigned to the brake pressure regulating system 22 and not illustratedseparately, detects that, for example, one of the driven wheels of thevehicle is spinning. The precharge pump 20, activated thereupon by thecontrol unit, then supplies to the first pressure chamber 40, via thehydraulic line 26, a specific admission pressure which may be, forexample, in the region of 3 bar. The throttle 60 arranged in the firstpressure chamber 40 prevents this precharge pressure from beingtransferred immediately into the reservoir 16, because the nonreturnvalve 72 remains closed and the throttle orifice 74, formed by theradial duct 86 in the basic body 76 of the throttle 60, allows only agreatly delayed transfer of pressure. In the first pressure chamber 40,therefore, essentially the precharge pressure generated by the prechargepump 20 builds up. Depending on the magnitude of the precharge pressuregenerated and the restoring force of the restoring spring 46, a specificprecharge pressure will also build up in the second pressure chamber 42.

The precharge pressure generated in the first pressure chamber 40 and,if appropriate, also the second pressure chamber 42 makes it possible,then, despite the brake master cylinder not being actuated, for thebrake pressure regulating system 22 to function correctly, thisprecharge pressure being supplied in the conventional way to the returnpump (not shown) of said system. A second exemplary embodiment of thebrake master cylinder 10, illustrated in FIGS. 4 and 5, is essentiallyfunctionally identical to the first exemplary embodiment describedpreviously, but differs in the arrangement of the throttle 60 and thereturn connection 30. In the second exemplary embodiment, the returnconnection 30 to be connected to the hydraulic line 26 does not openinto the first pressure chamber 40, but, via a duct 93, into the annularspace 54 preceding the pressure chamber 40 (see FIG. 4). The somewhatmodified throttle, designated therefore by 60', is arranged, in thesecond exemplary embodiment, in a widened end portion 94 of the duct 52which connects the connecting orifice 50 to the annular space 54. In thecase of the throttle 60', the nonreturn valve and throttle orifice areformed by a valve body 98 which is prestressed resiliently against aseat 96 and through which a duct 100 representing the throttle orificepasses axially. 84' designates a spring holding plate which is pressedinto that end of the duct 52 on the right in FIG. 5 and which holds thespring prestressing the valve body 98 against the seat 96.

In a third embodiment of the brake master cylinder 10, modified inrelation to the second exemplary embodiment, the throttle 60" is notlocated in the duct 52 of the master cylinder housing 32, but isdesigned in the form of an insert 102 which is inserted into a nipple104 of the reservoir 16, said nipple being provided for connection tothe connecting orifice 50. As emerges from FIG. 6, the insert 102consists of a cylindrical basic body 106 which has, at its outer end, arim 108 as push-in limitation and two axial passage recesses 110 and112. Inserted into the passage recess 110 on the left in FIG. 6 is aconventional nonreturn valve 114 which virtually does not impede anouthydraulic fluid stream from the reservoir 16, but blocks the returnhydraulic fluid stream into the reservoir 16. The passage recess 112 onthe right in FIG. 6 is greatly narrowed, at its end arranged in thereservoir 16, to form a throttle orifice 74'. According to the thirdexemplary embodiment, the throttle 60" may be integrated into aconventional brake master cylinder 10 without any appreciable designchanges.

In a fourth exemplary embodiment (see FIG. 7), the throttle 60" of thethird exemplary embodiment is integrated into a cruciform adaptor piece116 which is inserted between the reservoir 16 and the connectingorifice 50 of the master cylinder housing 32. In contrast to the firstthree exemplary embodiments, in the fourth exemplary embodiment thereturn connection 30 is not designed on the master cylinder housing 32,but on the adaptor piece 116. That connection of the adaptor piece 116which is located opposite the return connection 30 in FIG. 7 receivesthe hydraulic line 18 which is connected at its other end to the suctionside of the precharge pump 20. That connection of the adaptor piece 116which is at the top in FIG. 7 receives the one nipple of the reservoir16 via a rubber sleeve, whilst the opposite lower connection of theadaptor piece is likewise to be inserted into the connecting orifice 50via a conventional rubber sleeve. If the adaptor piece 116 is used, itis not necessary to make any design change to conventional mastercylinder housings.

Brake master cylinders 10 according to the second, third and fourthexemplary embodiments have the advantage of statistically greaterfailure safety of the vehicle brake systems, since the return connection30 does not open directly into the first pressure chamber 40.

We claim:
 1. Brake master cylinder for a hydraulic vehicle brake system,with a master cylinder housing and at least one pressure chamberdesigned therein, with a hydraulic fluid reservoir which is connected tothe at least one pressure chamber and which, furthermore, is providedfor connection to a precharge pump of a brake pressure regulatingsystem, and with a hydraulic fluid return connection which makes a fluidconnection between the delivery side of the precharge pump, thereservoir and at least the one pressure chamber, characterized in that athrottle is arranged in this fluid connection, said throttle notimpeding a hydraulic fluid stream out of the reservoir into the at leastone pressure chamber and throttling a hydraulic fluid stream from thereturn connection into the reservoir.
 2. Brake master cylinder accordingto claim 1, characterized in that the return connection, the onepressure chamber and the reservoir are arranged one behind the other inthe return flow direction of the hydraulic fluid stream and the throttleis arranged between the one pressure chamber and the reservoir.
 3. Brakemaster cylinder according to claim 2, characterized in that the throttleis arranged in the one pressure chamber.
 4. Brake master cylinderaccording to claim 1, characterized in that the return connection isconnected to an annular space which precedes the one pressure chamberand which is itself connected to the one pressure chamber and to thereservoir.
 5. Brake master cylinder according to claim 4, characterizedin that the throttle is arranged between the reservoir and the annularspace.
 6. Brake master cylinder according to claims 2, 4 or 5,characterized in that the throttle is arranged in a nipple of thereservoir.
 7. Brake master cylinder according to claim 1, characterizedin that the throttle is arranged in an adaptor piece which is locatedbetween the reservoir and the master cylinder housing and whichcomprises the return connection.